TOPLINE:

In a cohort study of more than 1 million individuals, influenza vaccination between the ages of 40 and 50 years was not associated with decreased risk for incident Parkinson’s disease compared with no vaccination.

METHODOLOGY:

• This population-based cohort study assessed whether influenza immunization at midlife (age, 40-50 years) is associated with a reduced risk for Parkinson’s disease, using the UK Clinical Practice Research Datalink Aurum database.
• Vaccinated individuals (n = 87,562; mean age, 43.85 years; 60.8% women) who received influenza immunization at midlife between 1995 and 2017 were propensity score-matched with an equal number of control individuals who did not receive influenza immunization at midlife.
• The outcome was incident Parkinson’s disease; a 2-year lag period was used to account for diagnostic delays and minimize the inclusion of individuals already developing the disease.
• The median follow-up duration was 13.0 years for vaccinated individuals and 11.5 years for unvaccinated individuals.

TAKEAWAY:

• No significant association was found between influenza immunization at midlife and the risk for incident Parkinson’s disease (hazard ratio [HR], 0.96; 95% CI, 0.76-1.22).
• The association between influenza immunization and Parkinson’s disease did not differ by age, sex, or prior vaccination history.
• Vaccination during the influenza season was associated with a potentially greater benefit than no vaccination; however, the results were not statistically significant (HR, 0.62; 95% CI, 0.33-1.15).
• Results varied over time since vaccination, with the lowest risk observed around 8 years post-vaccination (HR, 0.75; 95% CI, 0.52-1.08); however, the association was not statistically significant.

IN PRACTICE:

“Temporary decreases in PD [Parkinson’s disease] risk several years after vaccination and decreases in PD risk among those vaccinated during influenza season appear possible, although the respective findings did not reach statistical significance and thus require further investigation and replication,” the authors wrote. 

SOURCE:

The study was led by Antonios Douros, MD, Institute of Clinical Pharmacology and Toxicology, Charité-Universitatsmedizin Berlin, Berlin, Germany. It was published online on December 5, 2025, in JAMA Network Open.

LIMITATIONS:

Because the study was observational, unmeasured confounders could have influenced the findings. Vaccine exposure may have been misclassified because records were obtained from routine primary care, potentially diluting any true effect. Additionally, Parkinson’s diagnoses may have been misclassified.

DISCLOSURES:

No specific funding was reported. One author disclosed receiving personal fees from CSL Behring, Covis Pharma, Amgen, Novartis, and Panalgo, whereas another reported receiving grants from the Canadian Institutes of Health Research.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.